Remote Control of main station radio with handheld

This page describes a slightly tacky way of making a remote control setup for amateur radio. Its basically a small repeater setup for personal use. In the UK its now permissible under the terms of BR68. This setup is not the best of way of doing this, but its what I made from what was lying around.

The receive section is a Maxon 70cms handheld. This is powered from the main station radio and Yaesu ft7100 via a control box. The control box (pictured above in black) contains a small relay and an lm338 voltage comparator. The Maxon radio has been modified to give a small DC offset on the audio output when squelch is broken, this DC voltage is detected by the lm338 which in turn drives a relay. The relay is used to pull the -PTT line from the Yaesu radio to GND to key the transmitter.

The transmit half of the repeater is an old StandardC78 70cms radio. The display is very tired so I use it as a dedicated transmitter. After poking around inside I found its possible to wind the power down to about half a watt. To ensure the coverage is only local it transmitts into a slightly lossy dummy load.

The lossy dummy load is a 50ohm thinwire terminator (qtr watt style) with an inline attenuator and a T-piece. The T is just enough exposed metal on the pin to radiate a good signal for a few hundred meters, ample distance for this application. The black control box with two switches is used to key the transmit and also to switch on or off a speaker. One advantage of using older dumb equipment for TX side is that it doesnt have a transmit timout or any software to fight with.